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发布时间：2006-06-22 13:27     点击：

    (E) complimentary: fulsomeness

    The Food and Drug Administration has recently proposed severe restrictions on the use of antibiotics to promote the health and growth of meat animals. Medications added to feeds kill many microorganisms but also encourage the appearance of bacterial strains that are resistant to anti-infective drugs. Already, for example, penicillin and the tetracvlines are not as effective therapeutically as they once were. The drug resistance is chiefly conferred by tiny circlets of genes, called plasmids, that can be exchanged between dif- ferent strains and even different species of bacteria. Plasmids are also one of the two kinds of vehicles (the other being viruses) that molecular biologists depend of when performing gene transplant experiments. Even present guidelines forbid the laboratory use of plasmids bearing genes for resistance to antibiotics. Yet, while congressional debate rages over whether or not to toughen these restrictions on scientists in their laboratories, little congressional attention has been focused on an ill-advised agricultural practice that produces known deleterious effects.

    17. In the passage, the author is primarily concerned with

    (A) discovering methods of eliminating harmful microorganisms without subsequently generation drug-resistant bacterial

    (B) explaining reasons for congressional inac- tion on the regulation of gene transplant experiments

    (C) describing a problematic agricultural prac- tice and its serious genetic consequences

    (D) verifying the therapeutic ineffectiveness of anti-infective drugs

    (E) evaluating recently proposed restrictions intended to promote the growth of meat animals

    18. According to the passage, the exchange of plas- mids between different bacteria can result in which of the following?

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